Cell surface features of B cells

The unique B cell surface feature is the antigen receptor, formed in part by membrane immunoglobulin. Receptor assemblies of newly formed mature B cells contain immunoglobulin M (IgM) and/or IgD. B cells appropriately stimulated by interaction with T helper cells and their interleukin products may switch to production of other Ig classes, and the B cell antigen receptors then contain IgG, IgA or IgE, but not IgM or IgD. The H chain of receptor immunoglobulin is anchored in the membrane, in association with proteins Ig-a (CD79a) and Ig-|3 (CD79b). The intracellular domains of Ig-a and Ig-(3 participate in generating a receptor-mediated signal within the cell, transmitted through activation of protein kinases. Lyn (Src family) and Syk (Syk/Zap70 family) are protein kinases that associate with the resting B cell receptor and, along with additional kinases, participate in B cell activation pathways.

Other B cell membrane proteins regulate the intensity of responses that follow antigen binding (Table 1). Cross-linking of a B cell-specific complement-binding assembly (proteins CD19, CD21, CD81 and Leu-13) to the antigen receptor dramatically lowers the antigen concentration required for B cell activation. CD45, a positive regulator (perhaps an initiator) of signaling, is a transmembrane protein with a cytoplasmic tail that has essential phosphatase activity. Other phosphatases (e.g. SHP-I) are attenuating, and some membrane molecules (e.g. CD22, FcyR) increase the effect of attenuating phosphatases.

Additional B cell surface molecules have diverse functions, serving to present processed antigen fragments and costimulatory signals to T cells, mediate adhesion between B and T cells, or as receptors for cytokines produced by T cells (Table 2). B cell activation and class switching can be stimulated through

Table 1 B cell receptors and associated membrane proteins

Receptor complex




B cell antigen receptor (BCR)

IgM, IgD, IgG, IgA or IgE


Receptor-mediated signaling

How To Bolster Your Immune System

How To Bolster Your Immune System

All Natural Immune Boosters Proven To Fight Infection, Disease And More. Discover A Natural, Safe Effective Way To Boost Your Immune System Using Ingredients From Your Kitchen Cupboard. The only common sense, no holds barred guide to hit the market today no gimmicks, no pills, just old fashioned common sense remedies to cure colds, influenza, viral infections and more.

Get My Free Audio Book

Post a comment